Answer:
1992 (Early 1990s)
Explanation:
First of all, i would like to define an extrasolar planet as a planet that orbits a start that is not our own.
The first confirmed detections of extrasolar planets occured in the early 1990s (specifically 1992, some say 1995). The name of the first extrasolar planet is widely believed to be called Dimidium or 51 Pegasi b.
Extrasolar were searched by monitoring stars for slight dimming that might occur as unseen planets pass in front of them.
Balanced equation is:
2Mn+4CuCl——->4Cu+2MnCl2
a=2
b=4
c=4
d=2
